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Hi all, I am currently in the middle of a new build (roof is now on:)). 

I need to start making decisions on heating/plumbing and I wanted to get some advice before proceeding. My idea is to use off-peak power supplemented with a solar array to run 2x Sunamps for DHW and UFH.

The house will have a wood-burning stove, so although I will install UHF plumbing during construction, I might not utilize unless we feel we need it.

 

quick info:

- 2 bedroom Bungalow 120m2, well insulated (200mm EWI), triple-glazed, good air-tightness.

- I plan to use Sunamp UniQ9 HW+iPV for DHW and another for UHF (UHF will be in two bathrooms and kitchen approx 40m2) 

- 2.3kw solar array (flat roof mounted)
- wood burning stove 5-8kw
 


Some questions I have so far:
 

For DHW, am I right in thinking I need a unvented pressurised system for this set-up... as a pump is needed to draw water through the Sunamp?
 

Is there any need for an expensive solar PV diverter? Surely I can just have a switch with a timer for sunrise/sunset after the inverter?


Thanks everyone!!



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Take a look at this schematic from the Sunamp installation manual (this is from a UniQ eHW12, so may be subtly different).

 

No pump required PRV set to 3 bar

 

Without a PV diverter, your Sunamp will start charging as soon as the timer switches on, regardless of whether the sun is shining or not. By the time the sun comes out you could be fully charged from the grid and your opportunity to self consume your PV generation is lost for that day.

 

Most people say a PV diverter pays for itself relatively quickly. It's a must have really.

 

 

 

IMG_20210825_065555.jpg

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Sunamp for the UFH is pointless - use the slab as the store and use a Willis heater to provide the heat into the slab itself. You’re only load shifting from off peak anyway and a Sunamp is a resistance heater unit so there is no cost benefit and you’re unlikely to get the payback on installing it against direct heating the slab. 
 

You say UFH in the kitchen and bathrooms - what is heating the rest of the house ..? And how much insulation under the screed / slab..?

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11 hours ago, willbish said:

Take a look at this schematic from the Sunamp installation manual (this is from a UniQ eHW12, so may be subtly different).

 

No pump required PRV set to 3 bar

 

 

Thanks a lot for reply. So rising main directly into Sunamp is sufficient? ..but without power showers I'm guessing I would need to increase pressure after heating?

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31 minutes ago, westcoast said:

 

Thanks a lot for reply. So rising main directly into Sunamp is sufficient? ..but without power showers I'm guessing I would need to increase pressure after heating?


You can’t pump off a rising main anyway. And 3 Bar mains pressure is a lot ..!

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13 hours ago, PeterW said:

Sunamp for the UFH is pointless - use the slab as the store and use a Willis heater to provide the heat into the slab itself. You’re only load shifting from off peak anyway and a Sunamp is a resistance heater unit so there is no cost benefit and you’re unlikely to get the payback on installing it against direct heating the slab. 
 

You say UFH in the kitchen and bathrooms - what is heating the rest of the house ..? And how much insulation under the screed / slab..?

 

Thanks for your replies Peter, we will have MVHR and the house is well insulated + lots of thermal mass (block-on-flat construction with 200ewi) didnt see the need for every room to be heated, also in my experience living in a house with UFH, it was never used in bedrooms and very rarely in living room.. 

 

Just been reading up on some of your knowledgeable posts about Willis heaters, one thing comes to mind:

 

Most people seem to use Willis heaters to heat whole slab with E7, which would slow release throughout the day.. but we have insulation on slab and a 70mm screed. I wonder if the floor would still be warm in the morning? and would escaping heat just be trapped in our wall thermal mass anyway?

 

btw our 70mm screed only gives us space for 100mm insulation below, will have to use high performance, maybe PIR?

 

 

thanks again!

 

 

 

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48 minutes ago, westcoast said:

btw our 70mm screed only gives us space for 100mm insulation below, will have to use high performance, maybe PIR?

 

100mm of 0.035W/m.K EPS would for a 8m x 15m slab give a U-value of 0.21 which is better than the Part L1A limiting value of 0.25, but CO2 emissions are calculated on a basis of 0.13 and you would have to add extra insulation elsewhere to compensate. 100mmm of PIR would give U = 0.15 would require less if any extra insulation to compensate.

Edited by A_L
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16 minutes ago, A_L said:

 

100mm of 0.035W/m.K EPS would for a 8m x 15m slab give a U-value of 0.21 which is better than the Part L1B limiting value of 0.25, but CO2 emissions are calculated on a basis of 0.13 and you would have to add extra insulation elsewhere to compensate. 100mmm of PIR would give U = 0.15 would require less if any extra insulation to compensate.

very interesting, thanks for this, is that Irish code or UK I guess they are pretty similar anyway.

 

Sounds like PIR is probably a safe bet

 

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That's not enough insulation in Ireland. Your floor has to be 0.15 if using UFH. The Part L regulations for insulation and energy performance are a lot higher in Ireland. You should have a preliminary BER certificate done. That will say what you need to achieve.

 

Get rid of the screed and put the UFH pipes in the slab. That gives you 70mm extra insulation. Also don't know why if it's a new build you can't just dig down another bit. That will allow you to use cheaper but thicker EPS insulation instead of PIR which is a lot more expensive and currently in short supply in Ireland.

 

UFH pipes are cheap and easy to install but impossible to install later. Put them in everywhere. You don't even have to connect them up in the bedrooms but you can very easily later if needed.

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7 hours ago, Dudda said:

That's not enough insulation in Ireland. Your floor has to be 0.15 if using UFH. The Part L regulations for insulation and energy performance are a lot higher in Ireland. You should have a preliminary BER certificate done. That will say what you need to achieve.

 

Get rid of the screed and put the UFH pipes in the slab. That gives you 70mm extra insulation. Also don't know why if it's a new build you can't just dig down another bit. That will allow you to use cheaper but thicker EPS insulation instead of PIR which is a lot more expensive and currently in short supply in Ireland.

 

UFH pipes are cheap and easy to install but impossible to install later. Put them in everywhere. You don't even have to connect them up in the bedrooms but you can very easily later if needed.

Thanks for reply.. thats good advice re ufh pipes.. 

 

already 50% into build though so it will have to be PIR at this stage.. 

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I'll bet my bottom dollar that it's 150mm PIR with a u value of 0.15. Its a very common detail and the 70mm screen just happens to add up to 220mm which is the height of a block. 

 

With 70mm screed over 120m you still have 16 tons of "storage heater" if you run UFH pipes through it. Every degree you raise the temperature of the slab by is about 4.4kWh of energy added. 

 

Say your heating load at is 2.2kw if you manage to heat up your slab by 5 degrees on cheap night rate electricity your it'll keep your house warm for 10 hours. 

 

Thats my grasp of it anyway. Read @TerryE blog for a better explanation. 

 

Although you have a lot of heat storage capacity in your walls don't over estimate the effect it'll have on day to day life in your house. If your sitting room is 17deg it will take an age for the 20deg stored in the centre of the concrete wall to release its energy to the room. Practically by the time it does something else will have already heated the room or you'll have given up and gone to bed. In reality its only the first few cm of a wall that absorb and release any heat on a daily basis. 

 

 

The slab is slightly different in that actively heating it you are taking into account this time delay. If done well you can gently (and cheaply) heat your slab well in advance and enjoy the slow release later. However it's not much good if you need heat NOW! 

 

We didn't install any heating ( in Cork). Mostly due to be pretending to be brave (read stubborn) and also being tight. There was something like €7k uplift for UFH and a heat pump and at our very small heating needs I couldn't make it break even anytime before 25 years if ever. 

 

We'll have to see how this goes this winter with our single electric rad in the hallway but in hindsight I would have copied @TerryE and @Dudda and just done UFH and Willis heater with the option of a ASHP later if a cheap one appeared.  

 

 

With regard DHW we have a direct 300l UVC. This performs well leaving aside the issues we had with the plumbers.  I think I would get one with a spare ASHP coil and even larger capacity next time round. 

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On 26/08/2021 at 22:04, Iceverge said:

I'll bet my bottom dollar that it's 150mm PIR with a u value of 0.15. Its a very common detail and the 70mm screen just happens to add up to 220mm which is the height of a block. 

 
Thanks for the detailed reply, I was getting a bit worried about 100mm being enough insulation (we had originally left 150mm but had to make compromises..)

The online Kingspan calculator works out at 0.14 with 100mm insulation:

https://www.uvalue-calculator.co.uk/calculator/floors/ground floor/solid concrete - insulation below screed/0.5/100/

I could possibly go to 110mm insulation (achieving 0.13) if using a 55mm liquid screed - I suppose this would only create a 13 ton storage heater! But there is an obvious trade-off here with: more thermal mass and slower release vs. less heat loss overall
 

 

On 26/08/2021 at 22:04, Iceverge said:

Say your heating load at is 2.2kw if you manage to heat up your slab by 5 degrees on cheap night rate electricity your it'll keep your house warm for 10 hours. 

 

Thats my grasp of it anyway. Read @TerryE blog for a better explanation. 

 
Thanks this is great and puts it in perspective.. I think I saw a spreadsheet on here somewhere to calculate ones heating load/requirements, I should really find that and try to make a more precise estimate.

 

 

On 26/08/2021 at 22:04, Iceverge said:

The slab is slightly different in that actively heating it you are taking into account this time delay. If done well you can gently (and cheaply) heat your slab well in advance and enjoy the slow release later. However it's not much good if you need heat NOW! 

 

We didn't install any heating ( in Cork). Mostly due to be pretending to be brave (read stubborn) and also being tight. There was something like €7k uplift for UFH and a heat pump and at our very small heating needs I couldn't make it break even anytime before 25 years if ever. 

 

We'll have to see how this goes this winter with our single electric rad in the hallway but in hindsight I would have copied @TerryE and @Dudda and just done UFH and Willis heater with the option of a ASHP later if a cheap one appeared.  

.
The good thing for us is we have a small stove for heat NOW!  :) ... but I take your point, its a careful balancing act, your demand cannot exceed the cost threshold making all the effort redundant. Having to use the Willis heaters throughout the day would be a fool's errand.

That was brave move indeed, but I understand what its like to spend a lot of money on insulation. I want to gauge the performance of our house over a year or so before adding anything too fancy - hopefully the Willis heaters will be sufficient anyway.


I suppose my main concern now is

Screed thickness vs extra floor insulation, will a thinner screed make the Willis idea useless as the heat will escape shortly after off-peak hours.. ?




Cheers

Edited by westcoast
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You need the extra insulation. No point having a thicker screed if the heat goes into the ground and not the room. Have you windows and doors in? What stage are you at exactly to see if we can change floor level. Eg if you've a service cavity planned for the ceiling could that be reduced slightly to keep the same floor to ceiling height.

I'd also check with who's signing this off and the BER. The whole house has to meet a standard which the floor feeds into. If they had 150mm PIR originally in the floor and you've the external 200mm insulation finished that can't now be increased to offset the reduced floor insulation.

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9 hours ago, Dudda said:

You need the extra insulation. No point having a thicker screed if the heat goes into the ground and not the room. Have you windows and doors in? What stage are you at exactly to see if we can change floor level. Eg if you've a service cavity planned for the ceiling could that be reduced slightly to keep the same floor to ceiling height.

I'd also check with who's signing this off and the BER. The whole house has to meet a standard which the floor feeds into. If they had 150mm PIR originally in the floor and you've the external 200mm insulation finished that can't now be increased to offset the reduced floor insulation.

 

No chance to move floors: windows and doors are in. Large sliding patio door would catch on floor if raised. 

 

it was 150mm EPS originally planned, will check with our engineer, but 150eps and 100 pir roughly equivalent, no?

 

Not spoken to BER assessor yet, but it could be a good time to get in touch!!

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Can you post your calculations please. I reckon 150mm of EPS will be a u value of 0.21.  Regs in Ireland require 0.16 for UFH.  200mm EPS, or 150mm PIR. 

 

If you upgraded to kooltherm you could get away with 110mm.  And 65mm screed. I think reading the above height limitations you're stuck with this . 

 

 

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22 hours ago, Iceverge said:

 

If you upgraded to kooltherm you could get away with 110mm.  And 65mm screed. I think reading the above height limitations you're stuck with this .

 

 

You are right, sorry, I was assuming Kooltherm was just standard PIR insulation, I had looked at Kingspan a while back before we compromised and decided it would be our only option...

 

The question is, how can I calculate the heat release time for different thicknesses of screed?

 

.

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16 hours ago, westcoast said:

The question is, how can I calculate the heat release time for different thicknesses of screed?

 

You can't without knowing the starting conditions and the heating load of your house. 

 

Ideally you want a large mass heated just above the temp of the room for long slow release. High temp difference= fast heat transfer (think old fashioned radiators) Low temp difference= slow heat transfer.

 

However you're stuck with the slab you have it sounds like. You can improve its heat storage capacity by using an anhydritec screed (about 25%) or installing UFH pipes in your concrete walls too like on the continent. 

 

There after you'll need to minimise you heating load. The "good-airtightness" sounds like a bit of an afterthought. What are your targets? Also the stove will loose energy hand over fist whilst it's not in use. Do you need it? 

 

In practice at this stage I'd plumb to allow a heat pump and bin the stove. Probably not much of a cost difference and will ensure a warm house.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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5 hours ago, Iceverge said:

You can't without knowing the starting conditions and the heating load of your house. 

 

Ideally you want a large mass heated just above the temp of the room for long slow release. High temp difference= fast heat transfer (think old fashioned radiators) Low temp difference= slow heat transfer.

 

However you're stuck with the slab you have it sounds like. You can improve its heat storage capacity by using an anhydritec screed (about 25%) or installing UFH pipes in your concrete walls too like on the continent. 


Really interesting, thanks for that info, I need to accurately get a figure for my heating load. Will work on this over the week.

 

 

5 hours ago, Iceverge said:

 

There after you'll need to minimise you heating load. The "good-airtightness" sounds like a bit of an afterthought. What are your targets? Also the stove will loose energy hand over fist whilst it's not in use. Do you need it? 

 

In practice at this stage I'd plumb to allow a heat pump and bin the stove. Probably not much of a cost difference and will ensure a warm house.

 

For my 'good' Air-Tightness I am going to spend as much as budget allows, which means:

- Intello membrane internally, bonded to scratch coat on walls - careful taping to window reveals, doors etc
- Correct cable entry grommets used when membrane needs to be pierced
- Chasings and below screed wall to be coated with sprayable liquid sealant

 

Unfortunately the stove is an aesthetic decision and is 'non-negotiable', it is of decent quality though with triple insulated flue. 

 

 

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14 hours ago, westcoast said:

For my 'good' Air-Tightness I am going to spend as much as budget allows, which means:

- Intello membrane internally, bonded to scratch coat on walls - careful taping to window reveals, doors etc
- Correct cable entry grommets used when membrane needs to be pierced
- Chasings and below screed wall to be coated with sprayable liquid sealant

 

Unfortunately the stove is an aesthetic decision and is 'non-negotiable', it is of decent quality though with triple insulated flue. 

 

 

Sounds like you have a handle on it. PM me for a cheaper alternative to intello and their tapes etc if you like.

 

poujoulat flue? 

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